Abstract: The largest dam height of a high CFRD is 140 m. After the initial impoundment, leakage occurred behind the dam, increasing with the water level of the reservoir, and the maximum leakage volume reached 1 720 L/s.A series of new detecting techniques for leakage were adopted, including underwater sonar leakage detection, underwater high-definition video, tracer test, drilling coring, water pressure test, in-hole video, connectivity tests. By using these technologies, the leakage of the karst foundation and the slabs were detected, which laid solid foundation for its reinforcement construction.